1. Field of Invention
This invention pertains to porous or channeled ceramic structure and process for making same using fugitive fibers to produce the porosity.
2. Description of Prior Art
Typical prior art processes for generating porosity in a ceramic structure include phase removal with an etchant and removal of a fugitive particulate phase. In the first process, an acidic or basic etchant is used to preferentially remove an existing phase whereas in the second process, porosity is developed by the use of mild heat treatment to remove an organic phase. The prior art processes are characterized by the use of particulate materials which are removed to develop continuous or discontinuous pores.
The prior art processes have significant disadvantages. The etchant process results in a liquid or a sludge by-product which may be difficult to dispose; residual anion or cation deposits in pores following the use of the etchant; and a limitation in terms of compositions for which this type of process is possible. The heat process suffers from lack of control as to pore location; continuity and size due to the use of particulate precursors; and from irregularly shaped pores and surface finish of the pores.
A variety of military and commercial applications employ porous ceramic structures. These applications include solid state gas sensors for carbon dioxide, where various ceramic structures are typically used, and for oxygen, where titania is typically used; bioceramic medical implants where hydroxyapatite is used; solid oxygen fuel cells where strontium-doped lanthanum magnatite is typically used; positive temperature coefficient thermistors where barium titanate is typically used; solid/liquid/gas filtration where silicon carbide and titania are typically used; and transducer materials for sensors and biomedical applications where lead zirconate titanate is typically used.
In all the above noted applications, addition of porosity to the ceramic structures enhanced their performance or led to new applications.